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Oxytocin Revisited

Submitted by Marnia on Sat, 2008-02-23 17:31

In recent years scientists discovered that oxytocin – best known for its role in labor contractions1 - was also the neurochemical behind apparent monogamy (in prairie voles) and emotional bonding between parents and children, friends and lovers. An experiment showed that it increases the attraction between familiar mates (in hamsters), but not between unfamiliar potential mates. 2

Another study showed that oxytocin was critical to male sexual arousal, and that it increased female sexual receptivity.3

Oxytocin sounded like the most romantic stuff. Everyone wanted to know if it came in pill form. At last it seemed like humanity had a convenient scientific shorthand for discussing the increased wellbeing associated with intimate union and romance. The benefits could apparently all be lumped together as “the gains from increased oxytocin.” We kind of thought so too.4

The story got even better. Researchers learned that oxytocin may limit consumption of sweets,5 that it is associated with increased trust6 and “mind-reading,”7 and with partner support. It also seems to ease autism symptoms,8 and those of addiction and withdrawal.

Many tasks

However, new research reveals that oxytocin's effects are not all so heart-warming. Think of oxytocin as the cello in a symphony orchestra, with the brain as the conductor. Depending upon what other instruments are playing along with the cello (or not), the music is very different. In the symphony of the body the additional instruments are the other neurochemicals released - and the other nerve cell receptors activated in various locations in the body and brain.

Alas, the body's subconscious conductor is focused pretty much on fugues of reproductive melodies. When performing the pregnancy theme, the conductor focuses on birth and protection of the new organism. In the fertility fugue, the conductor may call for recklessness, even though it puts an organism at risk. (As you'll see below, it now appears that the oxytocin cello has a part in both of these programs.)

Controlled intercourse may be a way to direct the orchestra as a whole, by displacing the subconscious conductor with a more conscious one - who is not focused solely on reproduction. Controlled intercourse seems to ease the extremes of high and low dopamine, as well as surges of post-passion prolactin. (More in a moment.)

Oxytocin proves to have more complex functions every month. For example, high levels of oxytocin are associated with maternal anxiety and aggression toward intruders. High levels of oxytocin also show up in the blood of women in stressful relationships. One might have predicted just the opposite.

And sniffing oxytocin has also been associated with feelings of envy and gloating. Oxytocin appears to impair human memory. It also rises briefly in the blood at orgasm and drops right down again in humans.9 In female rats, the surge of oxytocin at mating actually appears to trigger regular surges of prolactin for two weeks thereafter.10

Some years back, oxytocin was found to be behind the monogamy of prairie voles, but it now appears that Mother Nature's mating program only promotes monogamy if it's “social monogamy.” Just because mates hang out together for life doesn't mean they are sexually monogamous. DNA tests show that both genders in monogamous animals frequently seek out additional mates, while their primary relationship remains in tact. Could this same program, which enhance the gene pool, create restlessness in human marriages, too?

A link between orgasm, oxytocin and prolactin

Recently, high levels of oxytocin were measured in the brains of male rats who had just mated, and the levels stay up for hours.11 So does it make the rats all cuddly? Hardly! It seems to be part of the reason that they scurry off looking for additional mates. Researchers find that the post-orgasmic rats engage in riskier than normal behavior, without their usual caution. When scientists chemically blocked the effects of oxytocin, the rats didn't do that.

So oxytocin turns out to be a likely player in the Coolidge Effect phenomenon, at least in rats. The researchers noted that in humans, men are more likely to nod off after sex. Yet some men certainly feel restless, and can't wait to leave after sex.

Not long ago, we read on the Internet that a doctor is giving talks on the possibility of prescribing oxytocin for better orgasms. We can't help wondering whether those orgasms will be followed by unpleasant mood swings due to subsequent prolactin surges. There's some disagreement about what moods prolactin is associated with after sex. Prolactin definitely rises after orgasm – and 400 percent more after intercourse, as opposed to following masturbation.12 In fact, prolactin is the most reliable hormonal marker of orgasm.

Some scientists argue that prolactin translates into feelings of wellbeing. They may base this view on the fact that higher prolactin seems to be one reason pregnant and nursing women are uncharacteristically calm during pregnancy. A friend once told us that his wife kept having children because she felt so great during pregnancy. Her usual anxiety was gone.

Yet, does high prolactin translate into feelings of wellbeing after sex (when there is no pregnancy)? Maybe not. Certainly it can create feelings of satiation after sex, and satiation offers short-term relief from sexual frustration. However, prolactin has an inverse relationship with dopamine – the neurochemical of desire. So prolactin may actually quell desire, possibly eroding the romantic bond between couples. Interestingly, women with higher-than-average prolactin (not pregnant) were unusually irritable. High prolactin also seems to be associated with sexual dysfunction in men.

Outsmarting Mother Nature

These days it would be misleading to reduce 'oxytocin' to shorthand for the benefits of sustained union – let alone the benefits of generous, non-goal-oriented affection. It would be more fair to characterize oxytocin's role as consistently serving biology's goals of more, and more varied, progeny. No surprise there! This is not to say that the benefits of union are insubstantial, or that oxytocin isn't at the heart of the benefits.

Marriage statistics show that companionship is good health insurance, and oxytocin may well be associated with that life-giving companionship. Moreover, there are new clues that less fertilization-driven sex and more affection may be a way around our hidden mammalian programming.

The researchers aren't yet asking the key questions, so the proverbial penny hasn't yet dropped. However, in recent research scientists actually scanned the brains of two women who were still in love with their husbands after ten years. It was telling that three of the four spouses in these couples began those successful marriages in middle age. (One man married a colleague twenty years his junior and is now 62.) Not to insult anyone's virility, but is it possible that these couples inadvertently stumbled upon the benefits of more affection with less hot sex - which younger couples evolved not to find?

Perhaps you remember this experiment, in which the oldest couple's wounds healed fastest because they bickered less than the younger couples. Less orgasmic sex perhaps? Couples who stay in love are statistically alarmingly few, and possibly the husbands are quite...mature. It may not be safe to leave true love in Mother Nature's hands - whether or not she's holding a bottle of oxytocin.